Experimental Investigation on Damage Mechanism of Guar Gum Fracturing Fluid to Low-Permeability Reservoir Based on Nuclear Magnetic Resonance

Abstract

The damage mechanism of fracturing fluids has always been the hot research topic in the development of low-permeability reservoir with hydraulic fracturing. At present, the research in this area is conducted mostly by the conventional core fluid flow test designed with industrial standards, less in the experiment operated from a microperspective. Against the reservoir cores with different permeability, and based on the results of SEM, mercury injection experiment, and core fluid flow test, this paper uses the technology of nuclear magnetic resonance (NMR) to systematically analyze the degree and rule of water-sensitivity, water-block, and solid-phase adsorption damage resulted from hydroxypropyl guar gum (HPG) and carboxymethyl guar gum (CMG) fracturing fluids, and proposes a comprehensive test method for evaluating the fracturing fluids damage to the reservoir. The test results show that fracturing fluid infiltrating into the core causes the increase of bound water, mobile water retention, and solid-phase macromolecule substance absorption inside the core in varying degrees, decreasing the reservoir permeability. The extent of reservoir water-sensitivity damage is positively correlated with the increment of bound water, and the extent of water-block damage is positively correlated with mobile water retention volume. The adsorption and retention of solid-phase macromolecule substance causes largest loss of core permeability, averaging about 20%, and it is main damage factor of fracturing fluids, the water-sensitivity damage causes 11% of core permeability loss, and the water-block damage causes 7% of loss. As the reservoir permeability doubles, the comprehensive damage resulted from guar gum fracturing fluid decreases by 14%. The comprehensive damage of CMG fracturing fluid to reservoir is 6.6% lower than that of HPG fracturing fluid, and the lower the reservoir permeability, the larger the gap between damage of CMG and HPG fracturing fluids. With the technology of NMR, the objective and accurate evaluation of various damages to reservoir resulted from fracturing fluids is realized, and the corresponding relation between damage mechanism and damage extent is established, which provides reference for research on improvement of fracturing fluid properties and reservoir protection measures.